In Japanese Patent Application Laid-Open No. 9-193506, there is disclosed an invention relating to “Noise masking apparatus and noise masking method in image formation apparatus”. This invention relates to a noise masking apparatus for a laser beam printer, a copying machine or the like, which has a sound-producing object having a drive mechanism, being a source of noise at the time of operation and generating masking sound for masking this noise, and a masking sound control unit which controls this sound-producing object to generate masking sound of a frequency in the range of including the main component frequency of the noise, so as to reduce uncomfortable feeling due to the noise.
In Japanese Patent Application Laid-Open No. 10-232163, there is disclosed an invention relating to “Tone quality evaluation apparatus and tone quality evaluation method”. This is for enabling evaluation of only the roaring sound, which is a gloomy noise of low-frequency random noise generated by an air flow system, such as exhaust sound, from the noise constituted by the sound of various tones of the image formation apparatus, to make the correspondence with psychological annoyance easy.
Similarly, in Japanese Patent Application Laid-Open No. 10-253440, there are disclosed a tone quality evaluation apparatus and a tone quality evaluation method which extracts only creaking sound, which is recognized as offensive sound to the ear and is a persistent pure tone quality generated by a scanner motor or a charging device, from noise constituted of sound of various tones of the image formation apparatus and performs evaluation.
In Japanese Patent Application Laid-Open No. 10-253442, there are disclosed a tone quality evaluation apparatus and a tone quality evaluation method which makes it possible to evaluate only “sha” sound, which is a high-frequency random noise due to rubbing of the sheet of paper, from the noise constituted of sound of various tones of the image formation apparatus.
In Japanese Patent Application Laid-Open No. 10-267742, there are disclosed a tone quality evaluation apparatus and a tone quality evaluation method which makes it possible to evaluate only the moaning sound consisting of pure sound having peaks in a plurality of adjacent frequencies especially due to beat of the drive system, from the noise constituted of sound of various tones of the image formation apparatus.
In Japanese Patent Application Laid-Open No. 10-267743, there are disclosed a tone quality evaluation apparatus and a tone quality evaluation method as described below. That is, in the noise constituted of sound of various tones of the image formation apparatus, if there is no pure sound or moan, that is, when there is no protruding component in the frequency wavelength, it is felt smooth. Based on this, when the annoyance felt by human is generally referred to smoothness, the apparatus and the method can evaluate the smoothness of sound.
According to the invention described in Japanese Patent Application Laid-Open No. 9-193506, it is considered that the noise level is increased, by adding the masking sound to this generated noise, not by reducing the generated noise.
There is a disadvantage in that it requires a sound-producing object for generating the masking sound, and a control unit and a speaker for generating the masking sound only while the sound to be masked is generated, thereby increasing extra space in the layout of the machine and increasing the cost considerably.
In the series of inventions relating to the above-described tone quality evaluation apparatus and tone quality evaluation method, only the tone quality evaluation method is proposed, and a tone quality improving method of the actual product is not described.
Recently, from a viewpoint of softness to the environment, there is an increasing interest in the noise problem, and there is an increasing demand for solving the noise problem of the OA equipment in offices. Therefore, attempts have been made for quieting down the OA equipment, and considerably quiet environment has been achieved than before. Currently, as a method of evaluating the noise in the OA equipment, there are generally used a sound power level and a sound pressure level (ISO7779). However, these levels indicate values of acoustic energy generated by the office equipment such as a copying machine and a printer, and hence the correlation between these values and the human's subjective discomfort with respect to the noise may not be good.
For example, when sounds having the same value of the sound pressure level (equivalent noise level Leq: a value obtained by averaging the energy over the whole measuring time) are heard and compared, there may be a difference in the discomfort due to a difference in the sound frequency distribution or the existence of impulsive sound. Further, even if the value of the sound pressure level is small, but if a high-frequency component or a pure sound component is included, the sound may be felt uncomfortable.
Therefore, in order to improve the future office environment, not only the evaluation and reduction of the OA equipment by the sound power level and the sound pressure level, but also evaluation and improvement of the tone quality are both necessary. For the evaluation and improvement of the tone quality, it is necessary to carry out quantitative measurement of the tone quality for understanding the current situation, and to measure how much improvement has been achieved before and after the improvement. However, since the tone quality is not a physical quantity, quantitative measurement cannot be carried out. Hence, it is difficult to set a target value.
When the tone quality is to be evaluated by human, qualitative expression is obtained, such as “the tone quality has been improved a little”, or “the tone quality has been improved considerably”, etc. Further, since there is a difference between individuals, the evaluation is different depending on the person, or judgment may be difficult whether the obtained result can be generalized. It is impossible to perform objective evaluation relating to whether there is actually an effect by the measures taken, or how much effect can be obtained, unless the tone quality is quantitatively expressed by physical properties.
Therefore, it is necessary to carry out subjective evaluation tests, and to execute statistical processing, to thereby quantify the tone quality.
There are psychoacoustic parameters as physical quantities for evaluating the tone quality. The representative parameters are as described below (unit is shown in the bracket). (For example, see “Seventh Lecture of Design Engineering/System Section, Design for the 21st century, Aim at innovative progress of the system!”, The Japan Society of Mechanical Engineers, Nov. 10 and 11, 1997, “Sound and Vibration and Design, Color and Design (1)” Section No. 089B.)
Loudness (sone):Size of audibilitySharpness (acum):Relative distribution quantity ofhigh-frequency componentTonality (tu):Tunability, relative distributiontity of pure sound componentRoughness (asper):Rough feeling of the soundFluctuation strength (vacil):Fluctuation strength,beat feeling.
And, other than the above, there has been proposed an instrument capable of measuring the psychoacoustic parameters, such as:
Impulsiveness (iu):Impact propertyRelative approach:Fluctuation feeling.
All the parameters have a tendency that with an increase of the value, the discomfort increases.
Among these, only the loudness is standardized by ISO532B. With regard to other parameters, the basic idea and definition are the same, but since the program and the calculation method are different due to individual research by measuring instrument manufacturers, it is natural that the measurement value differs in each manufacturer. Further, there are original parameters, such as impulsiveness and relative approach, developed originally by the measuring instrument manufacturers.
Noise generated by the OA equipment such as a copying machine and a printer is constituted of noise of various tones due to the complexity of the mechanism. For example, gloomy sound of a low frequency, high-pitched sound of a high frequency, strikingly generated sound and the like are generated from a plurality of sound source such as a motor, paper or a solenoid, while changing timewise.
Human judges these sounds comprehensively to judge whether it is uncomfortable. It is considered that the judgment is performed by executing weighting such that which part of the sound is related with discomfort. That is, there are a psychoacoustic parameter having large influence and a psychoacoustic parameter having small influence with respect to the discomfort, depending on the tone of the machine.
For example, with a high-speed printer having a large number of frequencies of impulsive sound, the impulsive sound is felt unpleasant and hence the relation between the impulsiveness and discomfort becomes large. With a low-speed and relatively quiet desktop printer, since the occurrence of the impulsive sound is few, the charging sound which occurs at the time of AC charging is felt unpleasant and hence the relation between the tonality and discomfort becomes large. Thus, the sound source to be felt unpleasant is different depending on the type of the printer. Therefore, the sound source which requires improvement in the tone quality may be different in a low-speed machine and a high-speed machine.
Accordingly, the tone quality can be efficiently improved by searching a sound source and the psychoacoustic parameter having a large improvement effect with respect to the discomfort, and dropping the psychoacoustic parameter by means of measures against the sound source of the unpleasant sound and transmission measures.
The objective evaluation of the tone quality becomes possible by combining the psychoacoustic parameters having a large improvement effect with respect to the discomfort, performing weighting to the parameters to form a tone quality valuation plan, and calculating the subjective evaluation value with respect to the discomfort. It is expected that the tone quality can be improved based on the objective evaluation.
Based on this idea, the present applicant filed an application in which the discomfort of the OA equipment is expressed by an equation of loudness (the size of audibility) and tonality (relative distribution quantity of a pure sound component), according to subjective evaluation tests and the multiple regression analysis, and a discomfort index S obtained by this equation is decreased by reducing the AC charging sound having high correlation with the tonality. According to this application, the tone quality can be improved in an image formation apparatus of 16 to 20 ppm (low speed). ppm denotes the number of copies per minute for an A4 lateral size.
The present applicant filed an application in which the discomfort of the OA equipment is expressed by an equation of loudness square and sharpness (relative distribution quantity of a high-frequency component), according to subjective evaluation tests and the multiple regression analysis, and a discomfort index S obtained by this equation is decreased by reducing the vibration noise of paper having high correlation with the sharpness. According to this application, the tone quality can be improved in an image formation apparatus of 45 to 75 ppm (high speed).
The present applicant filed an application in which the discomfort of the OA equipment is expressed by an equation of sound pressure level and sharpness, according to subjective evaluation tests and the multiple regression analysis, and a discomfort index S obtained by this equation is decreased by reducing the vibration noise of paper having high correlation with the sharpness. According to this application, the tone quality can be improved in an image formation apparatus of around 27 ppm (medium speed).
However, as described above, since the part which is felt uncomfortable is different depending on the speed, 3 types of tone quality evaluation equations exist. These three tone quality evaluation equations are respectively obtained by using the image formation apparatus of 16 to 20 ppm (low speed), 27 ppm (medium speed) and 45 to 70 ppm (high speed).
The tone quality evaluation value calculated by this tone quality evaluation equation is a value which predicts the grade of sound calculated from the result of subjective intercomparison of sound, and hence there is no unit, and is concluded within the range where the subjective evaluation tests are performed. Therefore, when the tone quality evaluation equation is different, even if the tone quality evaluation value is the same, the discomfort is different.
For example, even if the values calculated by the tone quality evaluation equation for low velocity layers and by the tone quality evaluation equation for medium to high velocity layers are the same, such as 0, the discomfort thereof is not the same.
In the three tone quality evaluation equations, there is a portion where it is not confirmed in the speed range. For example, it is not clear that in the ranges of from 21 to 26 ppm, and from 28 to 44 ppm, which equation should be used or should not be used.